Stent having a multiplicity of undulating longitudinals

ABSTRACT

A stent which is adapted for placement in the vessels of a human body is provided. The stent may be in the form of a thin-walled metal cylinder having a longitudinal axis. The stent has a proximal end and a distal end and includes a number of circumferentially relatively rigid portions. The relatively rigid portions are joined to each other by one or mor longitudinals which extend in a substantially longitudinal direction. At least a portion of at least one of the longitudinals has an undulating shape where a first relatively rigid portion is located at the proximal end of the stent and a second relatively rigid portion is located at the distal end of the stent.

FIELD OF THE INVENTION

[0001] This invention is in the field of stents for maintaining patencyof any one of a multiplicity of vessels of the human body.

BACKGROUND OF THE INVENTION

[0002] In the last decade, many different designs of stents have beenused to maintain patency of arteries and other vessels of the humanbody. In all such devices, hoop strength is an important characteristic.Specifically, the stent must have enough hoop strength to resist theelastic recoil exerted by the vessel into which the stent is placed. TheMass stent described in the U.S. Pat. No. 4,553,545 and the Dotter stentdescribed in U.S. Pat. No. 4,503,569 are each open helical coils. ThePalmaz stent described in the U.S. Pat. No. 4,733,665 is of the “chinesefinger” design. The Gianturco-Rubin stent currently sold by Cook, Inc,is another stent design which like the stents of Mass, Dotter and Palmazdoes not have any closed circular member to optimize hoop strength.

[0003] The ideal arterial stent utilizes a minimum wire size of thestent elements to minimize thrombosis at the stent site afterimplantation. The ideal arterial stent also possess sufficient hoopstrength to resist elastic recoil of the artery. Although the optimumdesign for maximizing hoop strength is a closed circular structure, noprior art stent has been described which has a small diameter whenpercutaneously inserted into a vessel and which expands into the form ofmultiplicity of closed circular structures (i.e. rings) when expandedoutward against the vessel wall.

BRIEF SUMMARY OF THE PRESENT INVENTION

[0004] The present invention is an expandable stent that can be used inan artery or any other vessel of the human body which, when expanded,forms a multiplicity of generally circular rings whose closed structureoptimizes hoop strength so as to minimize elastic recoil of the vesselinto which the stent is inserted. Furthermore, the structure of thestent in the present invention is initially in the form of foldedellipses or ovals which can be formed to a small diameter forpercutaneous insertion by means of a stent delivery catheter. The ovalsare joined to each other by either a straight or undulating shaped wireswhich are called “longitudinals” which serve to space the deployed ringswithin the vessel. Straight longitudinals are used in straight vesselsand undulating longitudinals can be employed in either straight orhighly curved vessels such as some coronary arteries.

[0005] Thus, an object of this invention is to provide a stent having amaximum hoop strength by the employment of closed, generally circularstructures which are in fact rings.

[0006] Another object of this invention is that the rings are initiallyin the form of ovals that can be folded to fit onto a cylindricalstructure at a distal portion of a stent delivery catheter.

[0007] Still another object of this invention is that the fully deployedrings are spaced apart by means of longitudinals which are eitherstraight of undulating wires that are placed to be generally parallel tothe longitudinal axis of the vessel into which the stent is deployed.

[0008] Still another object of this invention is that the pre-deploymentstent structure is formed as a single piece out of a metal tube having asmaller inside diameter as compared to the outside diameter of anexpandable balloon onto which the pre-deployment stent is mounted.

[0009] These and other important objects and advantages of thisinvention will become apparent from the detailed description of theinvention and the associated drawings provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a side view of the stent after it has been deployed;i.e., in its post-deployment form.

[0011]FIG. 2 is a transverse cross section of section 2-2 of FIG. 1illustrating how the longitudinals are joined to the rings.

[0012]FIG. 3 is a cross section at section 3-3 of FIG. 2 showing thejoining of a single ring to the longitudinals.

[0013]FIG. 4 is a side view of the stent prior to being mounted onto astent delivery catheter, i.e., in the form of an initial structure.

[0014]FIG. 5 is a transverse cross section of section 5-5 of FIG. 4illustrating how the longitudinals are joined to the ovals.

[0015]FIG. 6 is a side view of a pre-deployment form of the stentstructure in which the ovals have been folded into a small diametercylinder that is placed around a deflated balloon situated near thedistal end of a stent delivery catheter.

[0016]FIG. 7 is a partial side view of a pre-deployment stent structureshowing only two of a multiplicity of folded ovals formed around anexpandable balloon in which the ovals are folded in an alternativemanner as compared with FIG. 6.

[0017]FIG. 8 is a side view of a post-deployment stent structure whichutilizes two undulating longitudinals on opposite sides of the stent forimproved placement in curved vessels.

[0018]FIG. 9 is a side view,of a stent as etched out of a small diametermetal cylinder as a single piece of metal.

DETAILED DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a side view of the cylindrical stent 1 of the presentinvention shown in its post-deployment configuration. The stent 1 has amultiplicity of rings 2 which are spaced apart by four wires calledlongitudinals. As seen in FIGS. 1 and 2, at the top of the stent islongitudinal 4T, at the bottom is longitudinal 4B, at the left side islongitudinal 4L and at the right side is longitudinal 4R. Although FIGS.1 and 2 show 7 rings and 4 longitudinals, it is apparent that the stentcan be made longer by adding rings or increasing the separation betweenrings. In a similar manner, the stent can be made shorter by reducingthe number of rings or decreasing the spacing between rings. Alsovariable spacing of the rings is envisioned for accomplishing a varietyof purposes including increased hoop strength at a particular section ofthe stent. Also, it is envisioned that the two or more longitudinalscould be utilized for this stent design with a maximum number being 32.

[0020]FIGS. 2 and 3 illustrate the joining of the longitudinals to therings. Specifically the longitudinals can be placed into cutouts in theform of notches 5 located on the outside perimeter of the ring 2. Thelongitudinals can then be spot welded, adhesively bonded or joined byany variety of means to the rings 2. It is also envisioned that thelongitudinals could be placed on the inside perimeter of the ring 2, orholes could be mechanically or laser drilled through the ring 2 forplacement therethrough of the longitudinals.

[0021]FIGS. 4 and 5 illustrate a stent 1′ shown in one particular formin which it could be fabricated; i.e., in an initial structure form.Specifically, FIGS. 4 and 5 show that this initial form of the stent 1′is a multiplicity of parallel ellipses or ovals 2″ each oval having thesame minor axis dimension m and major axis dimension M. The oval's minoraxis passes through the center of the longitudinals 4L and 4R. Theoval's major axis passes through the center of the longitudinals 4T and4B. It is important to note that, if it is desired to have a finaloutside diameter D (as seen in FIG. 2) of the ring 2 after it is fullydeployed, then it can be shown that D is given by the equation

D ²=½(m ² +M ²).

[0022] To place the stent design of FIGS. 4 and 5 onto a balloon that ismounted near the distal end of a stent delivery catheter, it isnecessary to fold the ovals 2′ around that balloon. Specifically, thepre-deployment cylindrical stent 1″ can be formed-onto an expandableballoon 6 as shown in FIG. 6 by folding the ovals 2′ about the dottedline F (which is the minor axis of the oval 2′) as shown in FIG. 5Specifically, as seen in FIG. 4, the top and bottom of the ovals 2′could be held stationery while the side longitudinals 4R and 4L arepushed to the left which results in the pre-deployment structure whichis shown as the stent 1″ in FIG. 6. An optimum design has the foldedovals 2″ as shown in FIG. 6 with the stent 1″ being a cylinder whoseoutside diameter is equal in size to the minor axis dimension m. Whenthe balloon 6 of FIG. 6 is expanded, the pre-deployment stent 1″structure forms the post-deployment stent 1 structure having circularrings 2 as shown in FIGS. 1 and 2.

[0023] The stent 1′″ is an alternative embodiment for a pre-deploymentstructure of the stent of the present invention as it is placed onto aballoon. Specifically, FIG. 7 shows 2 folded rings 2′″ of a multiplering stent 1′″. The stent 1′″ being formed by holding the top and bottomof the stent 1′ of FIG. 4 stationery while pushing the longitudinal 4Rto the left and pushing the longitudinal 4L to the right. Like the stent1″ of FIG. 6, when mounted onto a balloon, the stent 1′″ has cylindricalshape with a diameter equal to the dimension m.

[0024] FIGS. 1 to 7 inclusive illustrate stents that employlongitudinals that are formed from generally straight wires. FIG. 8shows an alternative embodiment of a stent 10 that has two undulatinglongitudinals. Specifically, the left side longitudinal 14L (shown asdotted lines) and the right side longitudinal 14R are each undulatingshaped longitudinals. A stent such as stent 10 could have two or moreundulating longitudinals. Such a stent would bend more easily duringinsertion into a vessel and would be more readily adaptable forplacement in curved vessels such as some coronary arteries.

[0025] Typically, the rings and longitudinals of the stents would bemade of the same material. Typical metals used for such a stent would bestainless steel, tantulum, titanium, or a shape memory metal such asNitinol. If Nitinol is used, the stent would be heat treated into theshape at body temperature having circular rings 2 as shown in FIGS. 1and 2. The rings could then be distorted into ovals as shown in FIGS. 4and 5 and then mounted onto a stent delivery catheter which does notemploy a balloon but is of the more general shape described in thepreviously cited U.S. Pat. No. 4,553,545 by C. T. Dotter. Such a designwould provide the desired stent structure having a multiplicity ofgenerally circular rings instead of the Dotter design of a helicalspring which inherently has a lesser hoop strength as compared to thepresent invention.

[0026] It should be understood that once the ovals are folded onto astent delivery catheter, when they fully deploy, they do not formperfectly circular rings as shown in FIG. 2, but rather they are of agenerally circular shape. Such comparatively small deviations form anexactly circular shape do not appreciably decrease hoop strength becausethey are in fact closed structures that are almost exactly circular.

[0027] It should also be understood that at least part of the end ringsof the stent could be fabricated from or coated with a radiopaque metalsuch as tantalum or gold to provide a fluoroscopic indication of thestent position within a vessel. However, the other rings and thelongitudinals could be made from a much less dense metal which wouldprovide less obscuration of the central region within the stent. Forexample, the stent rings and longitudinals could all be fabricated fromtitanium or a titanium alloy except the end rings which could be formedfrom gold which is then plated with titanium. Thus, the entire outsidesurface of the stent would be titanium, which is known to be acomparatively non-thrombogenic metal while the gold in the end ringsprovides an improved fluoroscopic image of the stent extremities.

[0028] The dimensions of stent rings are typically 0.1 to 0.3 mm thick,with a width of 0.1 to 0.5 mm and an outside diameter D between 2.0 and30.0; mm depending on the luminal diameter of the vessel into which itis inserted. The length of the stent could be between 1 and 10 cm. Thewire diameter for the longitudinals would typically be between 0.05 and0.5 mm. Although the designs of FIGS. 1 through 7 inclusive illustrateseparate longitudinals attached to a multiplicity of rings, thisinvention also contemplates an initial stent structure which ischemically etched from thin-walled tubing having an oval transversecross section. Thus the oval and longitudinals would be formed from asingle piece of metal thus precluding the need for attaching thelongitudinals to the rings. In a similar manner laser or EDM machiningcould be used to form the stent from a thin-walled tube.

[0029] It is further anticipated that a pre-deployment stent structure20 as shown in FIG. 9 could be formed from a thin-walled cylindricaltube whose inside diameter is slightly smaller than the outside diameterof the balloon 6 shown in FIG. 6. A pattern such as that shown in eitherFIG. 6 or FIG. 7 could be photoetched onto a tin-walled metal cylinder.The one piece structure 20 shown in FIG. 9 has folded ovals 22 andlongitudinals 23T, 24B, 24R and (not shown) 24L. This pre-deploymentstent structure 20 could then be mounted onto the expandable balloon;the stent having sufficient elastic recoil to firmly grasp down onto theballoon. Another method to form the pre-deployment stent is by etchingthe correct pattern onto a thin, flat metal plate, then forming a tubefrom the plate and then making a longitudinal weld to form acylindrically shaped structure which is, in fact, the pre-deploymentstent structure 20 shown in FIG. 9.

[0030] Various other modifications, adaptations, and alternative designsare of course possible in light of the above teachings. Therefore, itshould be understood at this time that within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed herein.

What is claimed is:
 1. A post-deployment stent structure for maintainingpatency of a vessel of a human body comprising: a multiplicity ofclosed, generally circular rings, the plane of each ring being generallyparallel to the plane of each adjacent ring, the rings having a commonlongitudinal axis which is perpendicular to the plane of each ring andwhich longitudinal axis passes through the geometric center of eachring; and a multiplicity of elongated wire structures forminglongitudinals which longitudinals are fixedly attached to the rings soas to be generally parallel to the longitudinal axis of the rings. 2.The stent of claim 2 wherein the rings have a multiplicity of cutoutsfor the placement therethrough of the longitudinals.
 3. The stent ofclaim 2 wherein the cutouts on the rings are notches.
 4. The stent ofclaim 3 wherein the notches on the rings are located at the outsideperimeter of each ring.
 5. The stent of claim 3 wherein the notches arelocated at the inside perimeter of each ring.
 6. The stent of claim 2wherein the cutouts are holes drilled through the rings.
 7. The stent ofclaim 1 wherein the longitudinals are essentially straight wires.
 8. Thestent of claim 1 wherein at least two of the longitudinals are of anundulating shape.
 9. The stent of claim 1 wherein the longitudinals arewelded to the rings.
 10. The stent of claim 1 wherein the rings andlongitudinals are made from or coated titanium.
 11. The stent of claim 1wherein the end rings are more radiopaque as compared to any other ring.12. The stent of claim 1 wherein the stent is formed from a metal havinga shape memory characteristic.
 13. An initial structure that is capableof being formed into a pre-deployment stent structure which in turn iscapable of being deployed into a post-deployment stent structure forplacement within a vessel of the human body, the initial structurecomprising: a multiplicity of flat ovals, the plane of each oval beinggenerally parallel to the plane of all other ovals, the ovals having acommon longitudinal axis which is perpendicular to the plane of eachoval and which longitudinal axis passes through the geometric center ofthe ovals; and a multiplicity of longitudinals which are fixedlyattached to the ovals, the longitudinals being positioned onto the ovalsso as to be generally parallel to the longitudinal axis of the ovals.14. The initial structure of claim 12 wherein the ovals and thelongitudinals are formed from a single piece of metal.
 15. A generallycylindrical pre-deployment stent structure which is capable of beingdeployed into a post-deployment stent structure for placement within avessel of the human body, the pre-deployment structure being formed froman initial structure which consists of a multiplicity of flat ovals, theplane of each oval being generally parallel to the plane of all otherovals, the ovals also having a minor axis and a major axis and a minoraxis dimension and a major axis dimension; the ovals having a commonlongitudinal axis which is perpendicular to the plane of each oval andwhich longitudinal axis passes through the geometric center of theovals; and a multiplicity of longitudinals which are fixedly attached tothe ovals, the longitudinals being positioned onto the ovals so as to begenerally parallel to the longitudinal axis of the ovals; thepre-deployment stent structure being formed by folding the ovals arounda distal portion of a stent delivery catheter, the pre-deployment stentstructure being adapted to form a post-deployment stent structure havinga multiplicity of generally circular rings that are formed from theovals, the circular rings being joined together by the longitudinals.16. The pre-deployment stent structure of claim 15 wherein the ovals arefolded around an expandable balloon located near the distal end of thestent delivery catheter.
 17. The pre-deployment stent structure of claim15 wherein the ovals are folded around the oval's minor axis to form agenerally cylindrical shape that can be mounted onto a stent deliverycatheter.
 18. The pre-deployment stent structure of claim 15 wherein oneside of the ovals is folded in one direction and the opposite side ofthe ovals is folded in the opposite direction to form a pre-deploymentstructure of a generally cylindrical shape.
 19. The pre-deployment stentstructure of claim 15 wherein the outer diameter of the generallycylindrical pre-deployment stent structure is approximately the same asthe minor axis dimension of the oval.
 20. The pre-deployment stentstructure of claim 15 wherein the stent structure is a cylinder formedfrom a single piece of metal, the cylinder being slightly smaller in itsinside diameter as compared to the outside diameter of an expandableballoon located at a distal portion of a stent delivery catheter ontowhich the stent structure is mounted.